CHAPTER 27 Prokaryotes and the Origins of Metabolic Diversity

1. CHAPTER 27 Prokaryotes and the Origins of Metabolic Diversity

2. They’re (almost) everywhere! • Prokaryotes - earliest organisms on Earth and evolved alone for 1.5 billion years.. • Their collective biomass outweighs all eukaryotes combined by at least tenfold. • More prokaryotes inhabit a handful of fertile soil or the mouth or skin of a human than the total number of people who have ever lived.

3. Live in Extreme places - • Prokaryotes are wherever there is life and they thrive in habitats that are too cold, too hot, too salty, too acidic, or too alkaline for any eukaryote • Archaea - has extremophiles - ‘like’ extremes! Thermophile - remember these from PCR!! Fig. 27.1 Obsidian’s pool

4. Biological significance- • Some harmful - Diseases caused by bacteria include tuberculosis, cholera, STDs • Bacteria in our intestines produce important vitamins. • Prokaryotes recycle carbon, nitrogen between organic matter and the soil and atmosphere. • Prokaryotes and eukaryotes in symbiotic relationships (cellulose digestion and cows!). • Mitochondria and chloroplasts evolved from prokaryotes that became residents in larger host cells (endosymbiosis)

5. Diversity of prokaryotes • Structure and metabolism varies. • 400,000 to 4 million species.

6. Bacteria and archaea are the two main branches of prokaryote evolution • The archaea inhabit extreme environments and differ from bacteria in many key structural, biochemical, and physiological characteristics.

7. Size and shape of prokaryotes • Most prokaryotes - unicellular; diameters in the range of 1-5 um, compared to 10-100 um for most eukaryotic cells • Some species aggregate forming colonies, (division of labor) • The most common shapes among prokaryotes are spheres (cocci), rods (bacilli), and helices. Fig. 27.3

8. Prokaryotes have a cell wall outside plasma membrane • Prevents the cell from bursting in a hypotonic environment. • Most bacterial cell walls contain peptidoglycan, a polymer of modified sugars cross-linked by short polypeptides. • Archaea lack peptidoglycan.

9. Gram staining • Positive or negative

10. Gram stain identifies differences in cell walls of bacteria • Gram-positive bacteria - simpler cell walls, with large amounts of peptidoglycans. (not harmful usually) • Gram-negative bacteria have more complex cell walls and less peptidoglycan. (very harmful). An outer membrane on the cell wall contains lipopolysaccharides, carbohydrates bonded to lipids. Lipolysaccharide is antibiotic resistant and is not easily attacked by host - escape detection

11. Antibiotics like penicillin prevent cell wall formation • Many antibiotics, including penicillin, inhibit the synthesis of cross-links in peptidoglycans, preventing the formation of a functional wall, particularly in gram-positive species. Bacteria bursts from water entry!

12. Capsule - outside cell wall • Capsule, outside the cell wall (smooth bacteria of Griffith); protection • Capsules adhere the cells to their substratum. • They may increase resistance to host defenses. • They glue together the cells of those prokaryotes that live as colonies. Sex pili

13. Prokaryotic and Eukaryotic flagella • Prokaryotic - solid core of protein, no membrane, spinning ‘propeller’ • Eukaryotic - microtubules, covered by plasma membrane, oar like with a power stroke

14. A second motility mechanism is found in spirochetes, helical bacteria. • Two or more helical filaments under the cell wall are attached to a basal motor attached to the cell. • When the filaments rotate, the cell moves like a corkscrew. • A third mechanism occurs in cells that secrete a jet of slimy threads that anchors the cells to the substratum. • The cell glides along at the growing end of threads.

15. Prokaryotic genome and structure- 3. • No nucleus, only nucleoid without nuclear membrane. • Circular main chromosome - fewer genes than eukaryotes, less histones • Plasmid DNA - antibiotic resistance genes, replicate independently • No membrane bound organelles - so how do cyanobacteria photosynthesize and how do aerobic bacteria undergo cell respiration? • Plasma membrane has the required enzymes for both processes • Protein synthesis - overall the same but many factors/proteins involved are different

16. Prokaryotes grow and adapt rapidly • Prokaryotes reproduce asexually by binary fission (no genetic variation) • Transformation, transduction, conjugation, transposition, and mutation cause variation/recombination • Growth -’multiplication’ - doubles every 20 min. • Geometric growth indicates this rapid rise Fig. 27.9

17. Endospores can remain dormant for centuries! Prokaryotes form endospores • Unfavorable conditions - form endospores. • In an endospore, a cell replicates its chromosome and surrounds one chromosome with a durable wall. • While the outercell may disinte-grate, an endospore,such as this anthraxendospore, dehy-drates, does notmetabolize, andstays protectedby a thick, protective wall. Sterilization under high pressure and high heat kills endospores Fig. 27.10

19. Prokaryotes can be killed by antibiotics - drugs released by other microorganisms • Prokaryotes compete with other prokaryotes for space and nutrients. • Many microorganisms release antibiotics, chemicals that inhibit the growth of other microorganisms (including certain prokaryotes, protists, and fungi). • Humans use some of these compounds to combat pathogenic bacteria. • Antibiotic resistance is a growing problem!

20. -Photoautrophs (cyanobacteria) -Chemoautrophs -Photoheterotroph - Chemoheterotrophs Saprobes, decomposers that absorb nutrients from dead organisms, and Parasites, which absorb nutrients from the body fluids of living hosts • Phototrophs - use light energy • Chemotrophs - use chemical energy (H2S, NH3, Fe2+) • Autotrophs - only need CO2 as carbon source (for photosynthesis or chemosynthesis) • Heterotrophs - need at least one organic source of carbon Prokaryotes - nutrition

21. Examples - look here

22. Prokaryotes - nitrogen fixation (review) • Nitrogen - in the form of gas - not accesible to living things except PROKARYOTES! • Some chemoautotrophic bacteria convert ammonium (NH4+) to nitrite (NO2-). • Others “denitrify” nitrite or nitrate (NO3-) to N2, returning N2 gas to the atmosphere. • A diverse group of prokaryotes, including cyanobacteria, can use atmospheric N2 directly. • During nitrogen fixation, they convert N2 to NH4+, making atmospheric nitrogen available to other organisms for incorporation into organic molecules.

23. Nitrogen cycle

24. . Nitrogen fixing cyanobacteria are the most self-sufficient of all organisms. • They require only light energy, CO2, N2, water and some minerals to grow Fig. 27.11

25. Oxygen use in prokaryotes • Obligate aerobes - require O2 for cellular respiration. • Facultative anerobes - will use O2 if present but can also grow by fermentation in an anaerobic environment. • Obligate anaerobes - poisoned by O2 and use either fermentation or anaerobic respiration.

26. Photosynthesis in prokaryotes • The very first prokaryotes were heterotrophs(important). Where did they get NRG and Carbon? • From the pool of organic molecules in the “primordial soup” of early Earth.

27. Evolution of photosynth. & cell resp. Glucose might run out Anaerobic fermentation Absorbs glucose from primordial soup 1) Heterotroph Nonoxygenic photosynthesis Anaerobic fermentation Anaerobic fermentation Can make ATP using H2S/ chemicals 2) Chemoautotroph 3)Photoautotroph

28. Aerobic respiration Evolution of photosynth. & cell resp. Oxygenic photosynthesis Makes glucose using photosynthesis 4) Photoautotroph (cyanobacteria) Nonoxygenic photosynthesis Anaerobic fermentation Anaerobic fermentation Can make ATP using H2S/ chemicals 2) Chemoautotroph 3)Photoautotroph

29. First prokaryotes - only glycolysis (anerobic fermentation - heterotrophs) • Limited supply of glucose/carbon source • Natural selection of photosynthetic organism • Cyanobacteria ancestor used nonoxygenic photosynthesis (single photosystem using H2S?) • Cyanobacteria - 3.5 billion years old - oxygenic photosynthesis using double photosystem - PSII and PSI; O2 accumulation - 2.7 billion years ago • Aerobic Cell respiration used O2 to extract energy from photosynthesis end products.

30. Photosynthetic groups are scattered among diverse branches of prokaryote phylogeny. Fig. 27.12

31. Woese used signature sequences, regions of SSU-rRNA that are unique, to establish a phylogeny of prokarotes. Fig. 27.13

33. Archaea - extremophiles…. - “lovers” of extreme environments. • Archaea can be classified into methanogens (anaerobes, sewage treatment, guts of herbivores, greenhouse gas), extreme halophiles (high salt -Dead sea, red due to a pigment) and extreme thermophilies (deep sea volacanic vent, hot springs)

34. Prokaryotes- ‘bacteria’ diversity

35. Prokaryotes- significance 1. • Recycling - decomposers (organic to inorganic); and return organic compounds back to inorganic form Ex: Fix nitrogen - cyanobacteria! And release nitrogen back • Symbiosis - several types - mutualism (gut bacteria/termites, root nodules of legumes for nitrogen fixation), parasitism, commensalism

36. Read on your own from here….. • Some pathogens are opportunistic. • These are normal residents of the host, but only cause illness when the host’s defenses are weakened. • Louis Pasteur, Joseph Lister, and other scientists began linking disease to pathogenic microbes in the late 1800s. • Robert Koch was the first to connect certain diseases to specific bacteria. • He identified the bacteria responsible for anthrax and the bacteria that cause tuberculosis.

37. Koch’s methods established four criteria, Koch’s postulates, that still guide medical microbiology. (1) The researcher must find the same pathogen in each diseased individual investigated, (2) Isolate the pathogen form the diseased subject and grow the microbe in pure culture, (3) Induce the disease in experimental animals by transferring the pathogen from culture, and (4) Isolate the same pathogen from experimental animals after the disease develops. • These postulates work for most pathogens, but exceptions do occur.

38. Some pathogens produce symptoms of disease by invading the tissues of the host. • The actinomycete that causes tuberculosis is an example of this source of symptoms. • More commonly, pathogens cause illness by producing poisons, called exotoxins and endotoxins.

39. Exotoxins are proteins secreted by prokaryotes. • Exotoxins can produce disease symptoms even if the prokaryote is not present. • Clostridiumbotulinum, which grows anaerobically in improperly canned foods, produces an exotoxin that causes botulism. • An exotoxin produced by Vibriocholerae causes cholera, a serious disease characterized by severe diarrhea. • Even strains of E. coli can be a source of exotoxins, causing traveler’s diarrhea.

40. Endotoxins are components of the outer membranes of some gram-negative bacteria. • The endotoxin-producing bacteria in the genus Salmonella are not normally present in healthy animals. • Salmonellatyphi causes typhoid fever. • Other Salmonella species, including some that are common in poultry, cause food poisoning.

41. Since the discovery that “germs” cause disease, improved sanitation and improved treatments have reduced mortality and extended life expectancy in developed countries. • More than half of our antibiotics (such as streptomycin and tetracycline) come from the soil bacteria Streptomyces.

42. The decline (but not removal) of bacteria as threats to health may be due more to public-health policies and education than to “wonder-drugs.” • For example, Lyme disease, caused by a spirochete spread by ticks that live on deer, field mice, and occasionally humans, can be cured if antibiotics are administered within a month after exposure. • If untreated, Lyme disease causes arthritis, heart disease, and nervous disorders. • The best defense is avoiding tick bites and seeking treatment if bitten and a character-istic rash develops. Fig. 27.17

43. Today, the rapid evolution of antibiotic-resistant strains of pathogenic bacteria is a serious health threat aggravated by imprudent and excessive antibiotic use. • Although declared illegal by the United Nations, the selective culturing and stockpiling of deadly bacterial disease agents for use as biological weapons remains a threat to world peace.

44. Humans have learned to exploit the diverse metabolic capabilities of prokaryotes for scientific research and for practical purposes. • Much of what we know about metabolism and molecular biology has been learned using prokaryotes, especially E. coli, as simple model systems. • Increasing, prokaryotes are used to solve environmental problems.

45. The application of organisms to remove pollutants from air, water, and soil is bioremediation. • The most familiar example is the use of prokaryote decomposers to treat human sewage. • Anaerobic bacteriadecompose theorganic matterinto sludge(solid matterin sewage), whileaerobic microbesdo the same toliquid wastes. Fig. 27.18

46. Soil bacteria, called pseudomonads, have been developed to decompose petroleum products at the site of oil spills or to decompose pesticides. Fig. 27.19

47. Humans also use bacteria as metabolic “factories” for commercial products. • The chemical industry produces acetone, butanol, and other products from bacteria. • The pharmaceutical industry cultures bacteria to produce vitamins and antibiotics. • The food industry uses bacteria to convert milk to yogurt and various kinds of cheese. • The development of DNA technology has allowed genetic engineers to modify prokaryotes to achieve specific research and commercial outcomes.